The present invention relates to lower leg prostheses and methods of assembly and alignment of lower leg prostheses and more particularly to an improved apparatus and method of assembly and alignment.
Traditionally there are two types of lower leg prostheses, an external or exoskeletal apparatus and an internal or endoskeletal apparatus. The exoskeletal apparatus consists of a rigid leg component shaped in the appearance of the external human leg, attached to a foot. Traditionally, the leg component was constructed of solid wood, but now it is more commonly constructed of a resin or lightweight composite material formed around a solid structural foam interior. The composite laminate leg component is extremely lightweight, strong, and capable of supporting very heavy loads. The leg component is attached to the limb of a person through a socket. The leg component is attached to an artificial foot through a block in the ankle area. The ankle block is usually solid wood or structural foam and contains a fastening mechanism such as a bolt and nut fastener to attach the artificial foot and the ankle block is usually permanently attached to the leg portion through the laminate of the leg component.
The method of forming the exoskeletal leg apparatus and aligning the socket and foot for a particular patient traditionally involves an initial bench alignment based on the experience of the prosthetist constructing the apparatus. The alignment of the apparatus is extremely important to the effectiveness and comfort of the finished device. After the leg portion is cast and attached to the ankle block further alignment of this portion is impossible without cutting the cast portion and re-constructing it. The only adjustment easily made by the prosthetist after forming the exoskeletal leg is the minor adjustment of foot rotation made possible through the foot fastener. Thus, due primarily to the alignment difficulty, the modern trend has been away from the exoskeletal leg prosthesis toward a more adjustable endoskeletal leg.
The endoskeletal leg apparatus comprises a series of tubes, simulating the bones of the leg, connected via adjustable components to the artificial foot and covered by a cosmetic cover to look like a human leg. The endoskeletal components are traditionally lightweight metals interconnected with fasteners and adjustable components. The advantage of the endoskeletal leg is that all of the components remain adjustable and are easily maintained and replaced if necessary. The components have also been standardized by many manufacturers for easy interchangeability and modularity. The main advantage of the endoskeletal apparatus is the ability for the prosthetist to align the leg by adjusting the components after the leg is statically and dynamically loaded by the end user during a fit test process. The process includes attaching a completely assembled apparatus including a foot to a user and allowing the user to stand and walk on the leg to determine the proper alignment. During this process, minute adjustments are made perfecting the alignment of the leg resulting in a more comfortable and effective prosthesis. The disadvantage of the endoskeletal leg is its relative high cost, its weight, its complexity, its noise potential due to multiple interconnected metal components, its mechanical appearance, and its lower strength capabilities as compared to the exoskeletal apparatus.
Thus what is desired is an improved apparatus and method of constructing and aligning an exoskeletal leg prosthesis.
One aspect of the present invention is an ankle block for a leg prosthesis. The ankle block comprises an insert having a body with an upper mounting surface and a bottom interface surface opposite from the upper mounting surface. The insert body defines a central coaxial hole therethrough. An over mold is formed about an exterior of the body and extends upwardly therefrom defining a central cavity above the insert and above the upper mounting surface.
Another aspect of the present invention is a method of constructing an exoskeletal leg prosthesis. The method comprises the steps of forming a leg socket for receiving the leg of a user and affixing a temporary adapter to a bottom of the leg socket. An ankle block is attached to the top of a prosthetic wherein the ankle block includes an insert for attaching the block to the foot and an outer mold molded over the insert and having an upwardly extending portion defining a recess therein. A temporary adapter is affixed to an upper surface of the ankle block and an endoskeletal pylon system is attached to the adapters on the ankle block and the leg socket to create a temporary adjustable prosthetic leg. The endoskeletal pylon is adjusted to align the prosthetic foot with respect to the leg socket. After the prosthetic foot is aligned with the leg socket, the prosthetic foot is removed from the ankle block. The adjusted leg is retained in a fixture whereupon the endoskeletal pylon and temporary adapters are removed while maintaining the leg socket and ankle block in their adjusted alignment. A structural foam support is molded between the leg socket and the ankle block and then an outer structural shell is laminated to the combined leg socket, foam support, and ankle block. The prosthetic foot is then reattached to the ankle block.
Yet another aspect of the present invention is a method for constructing an exoskeletal prosthetic leg. The method comprises the steps of providing a leg socket and an ankle block affixed to a prosthetic foot. A temporary adjustable endoskeletal pylon is attached between the leg socket and the ankle block. The pylon is adjusted to dynamically align the prosthetic foot with respect to the leg socket. The pylon is adjusted in a dynamic fashion to align the prosthetic foot with respect to the leg socket. The aligned prosthetic leg is then clamped in a fixture and the temporary endoskeletal pylon is removed while maintaining the adjusted alignment of the leg socket with respect to the ankle block. An inner foam core is constructed between the leg socket and the ankle block and a laminated shell is then applied to an exterior of the combined leg socket, foam core, and ankle block.
These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.